Child view controllers are not added as children.

[markst]

The class sets up the child view controllers appropriately with
willMoveToParentViewController:
but then doesn't actually add the view controller as a child.

see:
https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/CreatingCustomContainerViewControllers/CreatingCustomContainerViewControllers.html